LANDSLIDE DELINEATION AND RELATIVE DATING USING HIGH-RESOLUTION LIDAR, ODGEN, UTAH

The Rainbow Gardens Landslide Complex (study area) is a well-known active landslide area in suburban Ogden, Utah at the mouth of Ogden Canyon. This area is a priority for landslide mapping because of recent landslide activity between 1987 to 1994 and close proximity to built structures. The purpose of this study is to determine if high-resolution 0.5-meter LiDAR can show enough detail to determine the relative date of slides and observe previously unknown features at the study area which is heavily vegetated and developed. This study used newly acquired 2013-2015 LiDAR data to identify and map individual slides in the study area. Landslides were mapped using existing geologic maps and digital terrain models (DTMs) were generated from the LiDAR data. Slope shade maps were created from the DTMs and scarps, toes, and flanks were outlined in order to observe distinct slides. Hummocky topography and relative surface roughness was used to distinguish five unique slides. Two landslide features were observed that do not appear on previous maps of the study area. One of these features is interpreted to be a previously unmapped landslide, the other feature is interpreted to be a new internal scarp within a previously mapped slide. A cross section of the new landslide showed a scarp, hummocky surface, and a toe, this is interpreted to be a slump. The surface roughness was distinct enough between the five landslides to determine relative ages of each slide. Slide A is from 1994 and is the most recent slide, Slide B was observed to be between 1987-1993, Slide C is younger than D, Slide D is older than 1980, and Slide E is a historical slide but younger than 10 kya. The study found that LiDAR can assist in distinguishing between the ages of the landslides and observe previously unmapped features in heavily vegetated and developed areas.